One type of tachyarrhythmia is ventricular fibrillation - an irregular and uncoordinated action of heart muscle fibers. The result of such action is a failure or impairment of the heart to pump blood.
Ventricular tachycardia is another type of tachyarrhythmia and is also an irregularity of the heart muscle, generally characterized by an abnormally fast and altered contraction pattern, which may in some instances itself lead to death in a few minutes. Supraventricular tachycardia occurs in the tissues of the heart above the ventricles, especially in the sinus node, the atrium, the atrioventricular (AV) bypass tract, or in the AV node. Such tachycardias, especially ventricular tachycardia, are subject to being accelerated into ventricular fibrillation by a number of known factors and stimuli, and hence their existence poses a latent or overt threat to continued life.
The importance of the foregoing is that ventricular tachycardia may, and ventricular fibrillation does, result in cessation of adequate pump function of the heart and sudden cardiac death. This is the leading cause of death of humans in the United States.
Various therapeutic means for controlling tachyarrhythmias have evolved. These include pharmaceutical compounds and compositions for suppressing tachyarrhythmias, implantable antitachycardia devices, and mechanical surgical procedures for the resection (removal by cutting) of heart tissue. Cardiac mapping techniques conducted during sinus rhythm and/or during induced tachycardia have made possible the identification of specific zones of heart tissue which are the foci of tachyarrhythmias. Such foci occur in many portions of the heart tissue, varying from person to person, and in normal tissue as well as in diseased tissue. Thus, cardiac mapping is an almost necessary diagnostic technique preceding the practice of the inventions set forth herein, but is to be performed on each patient on a case-by-case basis.
Although cardiac mapping has greatly improved the identification of the location of the foci of tachyarrhythmias, thus improving the success of mechanical resection surgery, most such foci occur where mechanical resection is difficult or impractical to perform. Alternative means for the ablation of tissue containing tachyarrhythmia foci have been attempted, e.g., cryothermia, and electrical energy delivered by means of electrode-bearing catheters. However, the therapeutic efficacy of electrical energy for treating ventricular tachycardia is still subject to debate among surgeons and physicians.
It would be desirable to have a device and method for ablation of diseased heart tissue that can be continuously monitored while in use, and that can be applied to the heart tissue in locations that are not readily resectable by current methods.
The present invention satisfies the foregoing desires, and provides for the control of tachyarrhythmias in living humans by ablating tissue in vivo by subjecting the heart tissue at a selected site to a laser beam having sufficient energy and for a sufficient time to create a focal lesion at such site. The site in question can be within an area on the inner or outer surface of heart tissue which has been previously located by cardiac mapping as causing an arrhythmia. For example, the site may be on the inside or the outside of a heart's ventricle or atrium, or in the atrioventricular groove. To effect ablation, the laser energy is transmitted as a beam and precisely directed to the selected site for direct impingement by means of an elongated thin optical fiber or fiber optic. The laser energy can be emitted in a series of short discrete pulses or continuously.